added MacFullScreen class to enable Mac OS X Lion full-screen feature

Done with Max Desyatov<max.desyatov@gmail.com>

Change-Id: I2c3ff188b5f05dc3b8ec106fec0db3766b43a205
Reviewed-by: Erik Verbruggen <erik.verbruggen@nokia.com>

src/plugins/coreplugin/mainwindow.h

@@ -127,6 +127,9 @@ public:
     bool isPresentationModeEnabled();
     void setPresentationModeEnabled(bool);
 
+#ifdef Q_OS_MAC
+    void setIsFullScreen(bool fullScreen);
+#endif
 signals:
     void windowActivated();